D20 Eternity uses d20 Modern, d20 Weapons Locker, d20 Menace Manual, d20 Future, d20 Past, d20 Apocalypse, d20 Cyberscape, d20 Future Tech, Call of Cthulhu d20, and associated web enhancements in one setting. The core of it combines some of the different mini settings in the various books. This is where magic, psychic powers, the supernatural, and high technology meet.

Unspeakable horrors roam the earth and the stars beyond, weavers of arcane and divine magic have been gathering power since the dawn of man, and the creatures from the Shadow have been making our plane their new home for over two millennia, the powers of the mind are awakening among the masses due to psychic manipulation of extraterrestrials, magical energies and natural or mad made radiation have cause odd changes in people, the scientific arts have made the mundane more than a match for any supernatural threat. This is strange new world and yet familiar in so many ways.

The heroes could be independent agents in the world or could belong to powerful organizations depending on the era of play. The Fellowship (which includes the sub orders, Knightly Order of St. Bartholomew, Knights of the Silver Dragon) is the primary power group for players in PLs 4 or less (but can be used at higher PLs as a secrete society). The Paranormal Science and Investigation Agency other known as PSI, specifically Department-7 (one of eight departments of the agency) is the power group that the PCs should belong to in PLs 5 and 6. The Star Law peace keeper agency maintains law and order through out the Galactic Colonies, they represent the best of the best of local system police and investigators, and this group is available in PL 7. PCs of any kind have a place in any of these groups.

The setting used and how they relate to each other break down as follows;

(PL 3) Age of adventure (d20 P) is the Renaissance past of this world with some changes. The worship of the great old ones is more wide spread and open and psionics exist back then too.

(PL 3-4) Shadow stalkers (d20 P) is the Victorian past with some changes, magic and psionics are more available. This is where the great old one cults goes underground and a shadow war develops between the fellowship and the six-fingered hand.

(PL 4-5) Pulp heroes (d20 P) is the WW II past of the setting with some changes, magic and Psionic classes are used. Replace scientist with techie or field scientist, the Nazis were influenced by hastur.

(PL 5) The Modern (d20 M & UA) era uses the concept from the Urban Arcana book that Shadow hunters, Agents of PSI, and Urban Arcana co-exist, department 7 is part of PSI which uses magic and Psionic agents as well as non humans and mundane, PSI vs. The six-fingered hand (which is a cult of cthulhu) the center point of this era.

(PL 5-6) Genetech/CyberRave (d20 F & C) is the near future era of the setting; it’s the same as the modern era but introduces replacements, moreaus, mutations, cybernetics, and PL 6 tech.

(PL 6-7) Bughunters (d20 F) is the future era where Earth has become one nation and has started to expand into space colonization, but in addition to friendly and hostile alien races they have uncovered evils as old as time.

(PL 7) Mecha Crusade/Star Law (d20 F) is the far future era of the setting that takes place just after a colonial civil war. PSI and its departments are a sub section of Star Law, since this is the highest PL of the setting and all the classes except that is on the excluded list (below) this era has the most options for play.

Here is the list of allowed Advanced/Prestige Classes organized by book and at which PL they become available (3-7):[edit]

Aside from the obvious skill and feat changes, wealth is half way represented in the game so using the wealth dollar conversion table in d20 Modern for buying stuff from the CoC book is a non issue. Character creation should always be handled using d20 Modern rules.
I don’t use sanity as I feel it detracts from the heroic nature of the game, and if you have a game where the players can play as androids, fraal, orcs, and other strange creatures why should seeing a deep one or byakhee be so traumatic.
Monster stats are easy enough to convert, just convert skills and feats as necessary and ignore sanity loss. The D&D conversion chapter also adds spell resistance to certain monsters.

Psychic Feats I allow with two changes, one obviously no sanity cost, and second change any reference to the psychic focus skill to concentration (a nod to Psionic focus from the XPH) having a high stat prerequisite and most of them have ability costs I find it balances fine (besides the sensitive feat seems to be more for GM use anyway).

Mythos Spells are tricky; they can only be learned and cast the way they are presented by the Occultist and Spiritualist, they still suffer the ability cost (damage or drain) with casting to keep it balanced (I even added ability damage cost to candle communication, chant of thoth, and detect life since without sanity they would be free).
In the D&D conversion chapter there is a section on adding mythos spells to spellcasters spell lists, use this handy guide to using this list the d20 modern spellcasters; Sor/Wiz is used for the mage, techno mage, and sorcerer. Clr is used for the acolyte, and the mystic. Drd is used for the shaman. Since spell casters have to use spell slots to cast them there is no “cost” to casting the spell, obviously they can’t use any spell above 5th level.

Fractional Base Save and Base Attack Bonuses House Rule from Unearthed Arcana. This fixes the one problem with multiclassing, having only two to three levels in three or more classes and winding up with low saves and BAB as a result.

Nonlethal Damage from the SRD, with MDT rules.

Dealing Nonlethal Damage: Certain attacks deal nonlethal damage. Other effects, such as heat or being exhausted, also deal nonlethal damage. When you take nonlethal damage, keep a running total of how much you’ve accumulated. Do not deduct the nonlethal damage number from your current hit points. It is not “real” damage. Instead, when your nonlethal damage equals your current hit points, you’re staggered, and when it exceeds your current hit points, you fall unconscious. It doesn’t matter whether the nonlethal damage equals or exceeds your current hit points because the nonlethal damage has gone up or because your current hit points have gone down.

Nonlethal Damage with a Weapon that Deals Lethal Damage: You can use a melee weapon that deals lethal damage to deal nonlethal damage instead, but you take a –4 penalty on your attack roll.

Lethal Damage with a Weapon that Deals Nonlethal Damage: You can use a weapon that deals nonlethal damage, including an unarmed strike, to deal lethal damage instead, but you take a –4 penalty on your attack roll.

Staggered and Unconscious: When your nonlethal damage equals your current hit points, you’re staggered. You can only take a standard action or a move action in each round. You cease being staggered when your current hit points once again exceed your nonlethal damage.
When your nonlethal damage exceeds your current hit points, you fall unconscious. While unconscious, you are helpless.
Spellcasters who fall unconscious retain any spellcasting ability they had before going unconscious.

Healing Nonlethal Damage: You heal nonlethal damage at the rate of 1 hit point per hour per character level.
When a spell or a magical power cures hit point damage, it also removes an equal amount of nonlethal damage.

Massive Nonlethal damage: If the amount of nonlethal damage from a single attack equals or exceeds your Massive Damage Threshold, you must make Fortitude save (DC 15). If you succeed on the save, you are dazed for 1 round. If you fail, you are unconscious for 1d4+1 rounds.

Epic Level Rules from the SRD;
Epic characters—those whose character level is 21st or higher—are handled slightly differently from non-epic characters. While epic characters continue to receive most of the benefits of gaining levels, some benefits are replaced by alternative gains.

Epic Save Bonus: A character’s base save bonus does not increase after character level reaches 20th. However, the character does receive a cumulative +1 epic bonus on all saving throws at every even-numbered level beyond 20th, as shown on Table: Epic Save and Epic Attack Bonuses. Any time a feat, prestige class, or other rule refers to your base save bonus, use the sum of your base save bonus and epic save bonus.

Epic Attack Bonus: Similarly, the character’s base attack bonus does not increase after character level reaches 20th. However, the character does receive a cumulative +1 epic bonus on all attacks at every odd-numbered level beyond 20th, as shown on Table: Epic Save and Epic Attack Bonuses. Any time a feat, advanced class, prestige class, or other rule refers to your base attack bonus; use the sum of your base attack bonus and epic attack bonus.
Class Skill Max Ranks: The maximum number of ranks a character can have in a class skill is equal to his or her character level +3.
Cross-Class Skill Max Ranks: For cross-class skills, the maximum number of ranks is one-half the maximum for a class skill.

Feats: Every character gains one feat (which may be an epic or non-epic feat at the player’s choice) at every level divisible by three. These feats are in addition to any bonus feats granted in the class descriptions.
Ability Increases: Upon gaining any level divisible by four, a character increases one of his or her ability scores by 1 point. The player chooses which ability score to improve. For multiclass characters, feats and ability increases are gained according to character level, not class level.

Table: Epic Save and Epic Attack Bonuses

Character Level Epic Save Bonus Epic Attack Bonus

21st +0 +1

22nd +1 +1

23rd +1 +2

24th +2 +2

25th +2 +3

26th +3 +3

27th +3 +4

28th +4 +4

29th +4 +5

30th +5 +5

Although most of the tables only show information up to a certain level (often 30th), that level is by no means the limit of a character’s advancement. It can be generally assumed that any patterns on a particular table continue infinitely.
Class Features: Many, but not all, class features continue to accumulate after 20th level. The following guidelines describe how the epic class progressions.
• A character’s base save bonuses and base attack bonus don’t increase after 20th level. Use Table: Epic Save and Epic Attack Bonuses to determine the character’s epic bonus on saving throws and attacks.
• Characters continue to gain Hit Dice and skill points as normal beyond 20th level.
• Generally, any class feature that uses class level as part of a mathematical formula continues to increase using the character’s class level in the formula. Any prestige class feature that calculates a save DC using the class level should add only half the character’s class levels above 10th.
• For spellcasters, caster level continues to increase after 20th level. However, spells per day don’t increase after 20th level. The only way to gain additional spells per day (other than the bonus spells gained from a high ability score) is to select the Improved Spell Capacity epic feat.
• The powers of familiars, special mounts, and fiendish servants continue to increase as their masters gain levels.
• Any class features that increase or accumulate as part of a repeated pattern also continues to increase or accumulate after 20th level at the same rate. An exception to this rule is any bonus feat granted as a class feature. If a character gets bonus feats as part of a class feature, these do not increase with epic levels. Instead, these classes get bonus feats at a different rate (described in each epic class description).
• In addition to the class features retained from non-epic levels, each class gains a bonus feat every two, three, four, or five levels after 20th. This augments each class’s progression of class features, because not all classes otherwise improve class features after 20th level. A character must select these feats from the list of bonus feats for that class. These bonus feats are in addition to the feat that every character gets every three levels. The character isn’t limited to selecting from the class list when selecting these feats.
• Characters don’t gain any new class features, because there aren’t any new class features described for these levels. Class features with a progression that slows or stops before 20th level and features that have a limited list of options do not improve as a character gains epic levels. Likewise, class features that are gained only at a single level do not improve.

Adding a Second Class: When a single-class epic character gains a level, he or she may choose to increase the level of his or her current class or pick up a new class at 1st level. The standard rules for multiclass characters still apply, but epic characters must keep in mind the rules for epic advancement. The epic character gains all the 1st-level class skills, and class features of the new class, as well as a Hit Die of the appropriate type. In addition, the character gets the usual skill points from the new class. Just as with standard multiclassing, adding the second class does not confer some of the benefits for a 1st-level character, including maximum hit points from the first Hit Die, and quadruple the per-level skill points. An epic character does not gain the base attack bonuses and base save bonuses normally gained when adding a second class. Instead, an epic character uses the epic attack bonus and epic save bonus progression shown on Table: Epic Save and Epic Attack Bonus.

Variant Sanity Rules from Unearthed Arcana. If sanity is used this would be how it would be used, for spellcasting I would used the moderate taint option, sanity resistance (equal to character level) would be available for PCs or NPCs that have hero levels, cthulhu mythos is renamed Knowledge (Forbidden Lore) and is only used to identify spells, objects, and creatures related to the great old ones and outer gods.

The nature of other planes of existence, elementals and outsiders:[edit]

d20 Modern, Past, and Future feature no planar travel, at not the kind controlled by the players. Most of the books feature outsiders and elementals, and one of the first questions is “how’d they get here?” To ease the excuse that everything comes from the Shadow (UA) or alternate dimensions (Future), I compiled a possible cosmology for this setting from information found in unearthed arcana, Menace Manual, d20 Apocalypse, and Call of Cthulhu.

1.) The Prime Material Plane; this consists of the universe as we understand it (galaxies, solar systems, planets, ECT.).

2.) The Shadow Plane; the contents of this plane is largely unknown. What is know for certain is that most supernatural creatures and magical power come from this plane, but so far travel though the plane is one way. If anyone has gone back through it they have not came back to tell.

3.) The Planes of Heaven and Hell; celestials and fiends come from each of these planes respectively, so far (according to religious beliefs) the only way to reach these planes is to die, it said that during the end time both of these planes will open onto the prime and let lose the “final conflict” between good and evil.

4.) Region of Dreams, realm of Nodens and his nightgaunts plus several other fell creatures, this is a plane of revelation, of discovery, and it is beyond the veil of your unconscious.

5.) Alternate dimensions; with a high enough level of technology (or magic) it is possible to travel to other dimensions that are radically different from our own where the known laws of the universe don’t apply and creatures with completely alien biology are the norm.

Mythos related outsiders and elementals often come from the depths of space, or dimensions far flung from our own, or the far distant past or future. Elementals are either native to the prime (but necessarily Earth) or come from the shadow, or possibly from an unknown elemental plane or planes. There is rumors of a plane of faerie where the sidhe and other fey are native to, but as of yet there are no known planar links.

Magic, psionics, and other supernatural powers have existed since humankind can remember. There have always been supernatural creatures and alien humanoids visiting and sometimes staying. This was a time where magic and the sword ruled but there were those of great power who had their eyes set on the world, and this brings us to the shadow wars. After blasting the world back to the Dark Ages the supernatural creatures tried to blend in and the aliens left for a while. Around the time of the Renaissance the supernatural and paranormal entities went into hiding to manipulate humanity from the shadows. Secret societies rose and fell during this time but some endured the test of time. After WW II the American government set up an agency to investigate paranormal occurrences. Shortly after the other worldly powers were proven completely magic, aliens and their kin were widely accepted and incorporated into the world at large. Several decades later globalization finally happened and the peoples of Earth as one reached out to the stars to replace their dying world. After many worlds were settled the colonists tried to break away from the government that birthed them, they lost. Now a broken but united interstellar frontier tries to rebuild what was lost, but is an ancient evil hungry for our souls is gnawing away the fledgling society from the inside.

This list is organized by alphabetical order and has notes at which PL it is founded (and ended if needed) and what book it appears in, factions of larger organizations are grouped beneath and tabbed to he left. This is not a list of every faction but a list of organizations that I feel best fit the setting.

This is a list of organizations from various d20 Modern books that I feel work best mythos cults.
I present them in alphabetical order with additional notes on which outer god/great old they most likely worship, and what book they appear in.